Physicians make use of catheters today in medical procedures to gain access into interior regions of the body for ablating targeted tissue areas. These procedures, called electrophysiological therapy, are becoming more widespread for treating cardiac rhythm disturbances. It is important for the physician to control carefully and precisely these ablation procedures, especially during procedures that ablate tissue within the heart. During electrophysiological therapy, the physician introduces an ablation catheter through a main vein or artery, typically the femoral vein or artery, into the interior region of the heart that is to be treated. Placement of the ablation catheter within the heart is typically facilitated with the aid of a guide sheath. The physician then further manipulates a steering mechanism to place an ablation electrode carried on the distal tip of the ablation catheter into direct contact with the tissue that is to be ablated. The physician directs radio frequency energy from the ablation electrode through tissue to an indifferent electrode, or another catheter-mounted electrode, to ablate the tissue and form a lesion.
It has been determined that an expandable and collapsible electrode structure is advantageous for ablation of body tissue within a patient's body. The electrode structure is maintained in a collapsed condition, i.e., in a low-profile condition, when inserting the catheter into and maneuvering the catheter through the vasculature of a patient. When the electrode structure reaches the target ablation sight, the electrode structure is expanded, i.e., in a large-profile condition. The expanded electrode structure allows larger and deeper lesions to be created in the body tissue. Alternatively, the expanded electrode structure allows vascular structures such as pulmonary veins to be electrically isolated from adjacent body tissue. In one implementation of an expandable and collapsible electrode structure, it has been proposed to manufacture the electrode structure out of a microporous material. An electrically conductive element is located within the interior of the electrode structure. In use, after the electrode structure is located at the target ablation sight, a medium containing ions is introduced into the interior of the electrode structure, causing the electrode structure to expand. High frequency RF energy is transmitted through the electrically conductive element and medium containing ions, to the body tissue for ablation of such tissue. Microporous electrode structures designed to automatically, consistently and easily fold upon itself when deflated can be introduced into the body through small introducing sheaths. Previous versions of the microporous electrode bodies collapsed into a somewhat larger profile and required a larger introducer for introduction into a vein or artery.